Understanding Automatic Software Update on Virtual Chassis Member Switches
You can use the automatic software update feature to automatically update the Junos OS version on prospective member switches as you add them to a Virtual Chassis.
Automatic Software Update Basics
When you have configured automatic software update on a Virtual Chassis, the Junos OS version is updated on the new member switch when you add it to the Virtual Chassis. The new member switch immediately joins the Virtual Chassis configuration and is put in the active state.
For a standalone switch to join an existing Virtual Chassis, it must be running the same version of Junos OS that is running on the Virtual Chassis primary. When the primary in a Virtual Chassis detects that a new switch has been added to the configuration, it checks the software version on the new switch. If the software version on the new switch is not the same as the version running on the primary, the primary keeps the new switch in the inactive state. If you have not enabled the automatic software update feature, you have to manually install the correct software version on each prospective member switch as it is added to the Virtual Chassis.
Automatic Software Update Restrictions
Refer to Feature Explorer to check support for automatic software updates, and the Junos OS release versions where the feature was introduced on each platform. Where the automatic software update feature is supported, see the Junos OS Release Notes for the release version running on the primary for any limitations in using automatic software updates between that release version and any prospective member switch release versions.